Hydraulic transmission



Dec. 26, 195@ H. ERNST ET Al.

HYDRAULIC TRANSMISSION Filed Nov. 27, 1944 Patented Dec. 26, 1950 HYDRAULIC TRANSMIS SION Hans Ernst and Albert H. Dall, Cincinnati, Ohio, assignors to The Cincinnati Milling Machine Co., Cincinnati, Ohio, a corporation of Ohio Appiication November 27, 1944, Serial No. 565,340

10 Claims. (Cl. Sil-21.5)

This invention pertains to hydraulic transmission and control mechanism for machine tools, and is particularly related to hydraulic feeding mechanism for milling machines.

One of the objects of this invention is to provide an improved hydraulic transmission and control mechanism for a milling machine feeding mechanism.

Another object is to provide a feeding mechanism for a milling machine which is responsive and automatically compensative to variations in the cutting forces developed during the machining cycle.

Still another object is to provide a hydraulic feeding system for a milling machine capable of effecting a smooth, uniform feeding movement between work and tool despite fluctuations in the cutting forces during the machining operation.

A still further object is to provide a down cutting milling device in conjunction with a locked hydraulic feeding system of a milling machine which automatically opposes any irregular or pulsating action in the relative feeding movement of work and tool during the cutting operation.

And a still further object is to automatically maintain any desired adherence to uniformity in the rate of travel of a hydraulically actuated member under the influence of varying forces applied thereto.

Other objects and advantages of the present invention should be readily apparent by reference to the following specification, considered in conjunction with the accompanying drawings forming a part thereof and it is to be understood that any modifications may be made in the exact structural details there shown and described, within the scope of the appended claims, Without departing from or exceeding the spirit of the invention.

Throughout the several views of the drawings similar reference characters are employed to denote the same or similar parts.

Figure 1 is a diagram including the hydraulic control circuit showing the application of the features of this invention to a milling machine hydraulic feeding system.

Figure 2 is a diagram illustrating the forward and back pressures in the hydraulic actuator for varying degrees of work resistance encountered during the cutting cycle.

In machine tools wherein a relative feeding movement of Work and tool is to be eifected, the work resistance due to the cutting action between the tool and the work surface reacts in rapidly varying amounts against the power being applied by the feed transmission. Because of this pulsating or intermittent variation in the lopposing force of the cutting action there is `diiiiculty in effecting a continuous smooth feeding movement between work and tool Which is necessary to produce the desired high degree of finish on a work piece. Particularly is this problem present in hydraulic feeding systems wherein the hydraulic actuator comprises a fluid pressure motor or cylinder to move a work or tool holder in feeding motion.

This invention is particularly adapted to minimize and substantially eliminate the effect of the fluctuating work resistance on the desired smooth feeding motion to be effected in the work carrier or table Ill, Figure l, of a milling machine. This table Ii! may be mounted for sliding feeding movement in any conventional manner on the milling machine frame. Preferably, a fluid pressure motor or actuator of the piston and cylinder type II, having a piston I2 and a piston rod I3 rigidly attached to the table I9 by suitable means I 4 is provided so that by reciprocating the piston I2 similar movements may be effected in the table SG. A suitable toolholder or rotary arbor kI5 carried by the conventional milling machine spindle is also provided upon which may be mounted the cutting tool or milling cutter I6 for rotation thereby while a work piece W mounted on the work table Ill is fed relative to it by means of the actuating cylinder II..

The piston i2 in the cylinder Il is actuated by fluid pressure pro-vided by a low pressure gear pump or rapid traverse pump I9 driven by a suitable prime mover (not shown). This pump I9 receives uid through a suction line I8 from the fluid supply reservoir Il and transmits fluid under pressure to a supply line Z connected to a selector valve 2l. A branch line 22 from the line `2@ is connected to a reiief valve 22a which, in turn, is connected to a drain line 25 for return of nuid to the reservoir II.

The selector valve 2i may be of usual design and operated by a suitable control handle 26 operable to a feed .eft position 2th and a rapid traverse left position itc, and to a feed right position 25d and a rapid traverse right position 2te. A stop valve 23 having a control lever 29 movable to a stop position 29d and to a run position 29h is provided to arrest movement -of the work table I0. When the table is stopped, uid pressure from the line 2i] is connected through the selector valve 2|, the line 23 to the low pressure relief valve 2li and returned to the reservoir il by the drain line 25 so that under these conditions the rapid traverse pump is discharging under very low idling pressure to thereby avoid unnecessary Waste oi power and heating of the hydraulic fluid,

When the selector valve is moved into the rapid traverse left position E-Ec for rapid movement of the work table lil, pressure from the rapid traverse pump i9 and the line 2li is cut on" from the line 23 and the low pressure relief valve 2d and is then connected to the line 2l which, in turn, is connected to the stop valve With the lever 2o of the stop valve the run position 29h the line 2l will communicate with the line 3s connected to the chamber Si of the main hydraulic actuating motor or cylinder l l. At the same time the line 32 connected to the chamber 33 of the cylinder l'i will be connected through the stop valve 23, the line 3d, the selector valve 2l, and the line 23, through the low pressure relief valve to the drain line 25 for return of expelled fluid to the reservoir il. Thus, under these conditions rapid application of fluid pressure up to the limit of the setting or the relier valve 22a may be utilized to actuate the piston l2 rapidly in the cylinder l l for effecting rapid traverse movements to the left, Figure l, in the Work table lil. By moving the control lever 2@ of the selector valve 2l to the rapid traverse right position 25e pressure from the line all will then be connected through the line 32 to cylinderll, discharge from the cylinder talring place out through the line 3u, the stop valve 26, the line 2l, the selector valve 2 l, the line 23, lov,T pressure relief valve 2li, and line 25 to the reservoir il. At any time, by moving the control lever 29 of the stop valve 23 to the stop position 2da, both of the lines 3c and 32 of the cylinder l'l may be blocked oi to arrest motion of the piston l2.

Preferably, a locked hydraulic feeding system, such for example as that shown in Patent 2,019,486, issued November 5, 1935, is provided for the hydraulic or fluid pressure actuator motor which includes cylinder l l. This locked hydraulic feed circuit includes a variable delivery fluid pressure pump receiving a supply of fluid from the line through a check valve and the line 3l' connected to the intake of the pump. The pump discharges into the line connected to the se lector valve 2l s-o that when its lever 2t is moved to a feed iorrvard position this line Will be connected to the line 2l, through the stop valve 2S, to the line to apply pressure in the chamber Si o the cylinder l l. Ait the same time, discharge from the chamber oi the cylinder ll will be connected through the line 32, stop valve 2i), line and the selector valve through line to the intake side of the variable delivery pump 35 so that fluid is positively applied in the chamber 3l and positively withdrawn from the chamber ci the cyl' so as to definitely control motion or" the piston i2 by the relative displacement effected in the chambers of the cylinder by the pump 35.

A high pressure constant delivery booster pump Zed to keep the circuit interconnected the variable delivery prunp and the v 's 3l and 33 oi the cylinder ll properly ith :duid at all times. This pump is to be supplied from the line 2li or the rges into line connected to the line 353 to in this way maire up any leakage which may occur in the feeding circ t. -luid is also supplied to the line directly from the gear pump line lf3 through a checir valve. l2 to further assist in keeping this line charged with fluid at all times. It is to l e noted that both of the check valves 36 and d2, however, prevent the high pressure ultimately developed by the variable delivery pump :i5 in conjunction with the booster pump from escaping back into the low pressure supply line 2o. t is to be also noted that by moving the control lever 2t oi the selector valve to the feed right position iisd the opposite direction of feeding to the right, Figure l, Will be effected in the piston l2 'by connecting line 3S through the selector valve 2i, to line til, stop valve 2S and line 32 to the chamber 33 in the cylinder l l while con necting the chamber 3l of the cylinder through line stop valve 28, line 2l, selector valve 2l, and line through the low pressure relief valve 2li to the line 25 for discharge into the reservoir il.

In connection with this locked hydraulic feeding circuit there is provided a differential relief valve'i?A for eilecting a complementary pressure rise and fall in the chambers 3l and 33 of the actuating cylinder i l in a manner as fully set forth and described in Patent 2,028,766, issued January 28 i936. Pressure fluid from the line 38 from the variable delivery pump 35 is connected by a line is to a chamber d5 in the dilerential valve from where it may escape past the end ci a spring-urged plunger le slidably mounted in the valve into a drain line All for return of Huid to reservoir This plunger is urged in opposition to the pressure in the chamber l5 by a compression spring et* so that as pressure increases in chamber d'5 the plunger will be moved aviaily so as to compress the spring d8 and when pressure drops in the chamber d5 the plunger will be moved by the spring is to tend to close the escape or" fluid from chamber e5 into the drain line il to thus maintain pressure in the lines :is and 88. in addition to this pressure control there is also provided a seco-nd pressure chamber i9 behind the valve plunger i5 which is connected by line through a luid resistance 5l to the line 3l of the intake side of the variable delivery pump 3-5.

Pressure changes, in the chamber 49 as effected by changes in pressure in the line 3l likewise operate in the same direction that pressure changes in the chamber d5 operate to oppose the spring 43. Thus, there is provided a dual pressure control p for the plunger [le both opposing thel spring 48,

one connected to the pressure line 3B and the other connected to the line 3l of the variable delivery pump 35. By appropriately proportioning the chambers [i5 and i9 so that the respective areas of the plunger it in these chambers bear a predetermined desired relationship any degree of sensitiveness of control of complementary pressure iluctuations in both the lines 3l and 38 is obtained. In this Way the sum of the forward and back pressures in the respective linesl 3f@ and 3l will remain substantially constant. A rise in forward pressure will, therefor@ be accompanied by a drop in the back pressure and vice versa.

When the control lever 25 is moved to a leed forward position 2Gb and pressurel from the line 38 of the variable delivery pump 35 is connected to the chamber 3l of the cylinder ii and discharge from chamber 33 is connected to the intake line 3l of the variable delivery pump, a :pressure differential must exist between the chambers 3l and 33 to eiect movement of the piston l2 to the left, Pressure in the chamber 3l must be in excess of that in the chamber 33 a suicient amount to overcome the frictional forces of the sliding of thev Work table lo on the milling mathe work table lilin the direction of feed and thereby tend `to `move the piston `toward the chamber 33 andaway from the chamber 3| with the result that pressure `will build `up in the chamber 33 and drop in the chamber 3|.

Obviously intermittent forces may develop` be-` tween cutter and `work under these conditions wherein the cutter at one time is assisting the work table as the teeth `engage the Work but wherein the work table must be moved solely by pressure in the chamber 3| when the tooth intermittently leaves the .work W. There is, `therefore, a constant change of pressure in thechamber 3| as the cutting cycle proceeds. In cases where down cutting milling is taking place usually the pressure in thechamber 33 will be relatively higher than under conditions where the table is being fed idly with no work in` engagement with the cutter. Also, in the instance where normal upcut milling is` to be undertaken, as shown at |511 and indicated by the arrow 53, the cutter has its teeth rotating in the opposite direction from that of the feeding motion of the table. In this case the pressure will be greater in the chamber 3| during `the'normal cutting operation whereas the pressure `in the chamber 33 will be relatively lower. l l c l The differential or complementary pressure conditions with respect to the cylinder chambers 3| and 33 of the cylinder for different degrees of positive or negative work resistances is illustrated in the diagram Figure 2 where it can be seen that the pressures cross at a point 54 (neglecting friction of the table slide) where no cutting is taking place. `When down cut milling takes place negative work resistance is encountered, i. e., work resistanceassisting the feeding motion, pressure in chamber 3| drops below pressure in chamberf33. l In up cut milling where the work resistance is opposed to the feeding motion the pressure in the chamber 3| will be greater than in the chamber 33. Any degree of variation of these pressuresmay rapidly take place in a pulsating uctuating manner due to the intermittent action of the cutting teeth of the cutter and the vibratory frequencies of the machine structure, resulting in corresponding pressure changes in the chambers 3| and 33 of the cylinder l.

It is these rapidly fluctuating pressure changes in the cylinder l which give rise to the undesirable uneven and irregular feeding movement of the work table lll. To eliminate this non-uniform motion of the work table |l by the piston |2 the fluctuations in pressure in the chambers 3| and 33 are utilized to control or modulate a hydraulic opposer mechanism connected to the work table l@ in such a manner as to automatically oppose the irregular fluctuations or backlash movement set up in the table ,by the cutting action and thereby produce a smooth uniform feeding motion between work and tool.

These fluctuations in pressure in the chamber 3| and 33 are ofrapid changing and minute character and are due largely to the compressibility of the relatively large volume of hydraulic fluid required in the cylinder While the variable delivery pump together with the differential valve 43 is capable of maintaining constant volumetric withdrawal from the cylinder uniformgravil metric` `withdrawal therefrom cannot -be steadily maintained because of pressure fluctuations and the minute compressibility of the hydraulic fluid. 5 To overcome this problem there is provided a hydraulically actuated mechanism for opposing these fluctuating feeding'movements` in which a minimum of hydraulic fluid is required in the opposing or compensating apparatus sothat the compressibility `of the fluid and its effect onthe positive controlling function to be performed is reduced tot. a minimum. A` hydraulic backlash opposer motor, such as the multiple cylinder rotary type pump or motor indicated generally at 55, is preferably used and may be suitably mounted on the milling machineframe. A mechanical transmission comprising themotor pinion 56 and the` gearing 51 connected to a rack 58 Xed on the work table Ill positively connects the motor 55to the work table. t In this way reciprocation of the work table I0 by the cylinder ll effects` driving rotation ofthe hydraulic motor 55.

When feeding motion is taking place the hydraulicmotor is driven to circulate fluid under pressure betweenthe lines 53 and Eil, each of which `is supplied from the pressure line 2D of the rapid traverse pump I9 through a line 6| and the respective check valves 62 and E3 so as to maintain these lines at all times charged with fluid. A backlash modulating control valve 66 is provided having a pressure chamber 65 connected to the line 63 by means of a branch line S4 so as to apply iluid pressure from line 60 behind the plunger 51 of this valve. A compression spring 68 behind the other end of the plunger opposes the pressure in the chamber 65. A discharge passageway 69, connected to the line 59 by a branch line has an edge '1| cooperating with the end 12 of the plunger 6l to form a variable fluid resistance to flow between the lines 64 and 'I0 in accordancefwith the axial positionof the plunger. A second pressure chamber 13 is provided in the valve 66 operating against the plunger 5l to also oppose the compression spring 68 and is con- .,f, nected by a line lll to the line 3|) which is in comrlnunication with the chamber 3| of theV cylinder A second backlash modulating valve 'l5 of the same construction as that of the valve 5G `is provided for controlling feeding movements in the opposite direction. This valve 15 has a pressure chamber 'IS connected by aline Tl to the line 59 so that pressure changes in the line 59 may react against the end 18 of the plunger 1S of the valve to oppose the compression spring B operating against the other end of the plunger. A discharge passageway 8| connected to the line 5B by branch line B2, has an edge 83 cooperating with the end 'i8 of the plunger 19 to form a varia- 60 ble fluid resistance to ow between the lines 17 and 82 in accordance with the axial position of the plunger 19. `A second pressure chamber 84 is also provided in the valve '|5loperating against the plunger 'I9 to also oppose the compression 05 spring 8U and is connected by a line 85 to the line 32 which, in turn, is connected to the charnber 33 of the cylinder ll. These valves 66 and l5 provide fluid pressure control means reacting on the closed hydraulic circuit 59-60 of the op- 70 poser motor variably to determine its resistance to tablemovement.

When the table I is being fed to the left, Figure 1, by` positioning the control lever 22B of the selector valve 2| in the position 26h, the hydraulic backlash opposer motor 55 is so arranged `that iiuid will enter the motor from the line 59 and be discharged out through the line d. As the feeding initially takes place with the Work not yet in contact with the cutter Iii there wili exist a pressure in chamber Si of the cylinder l l as indicated at 86 in Figure 2 and a pressure inchamber 33 of the cylinder as indicated at 8l, there being a small difference in pressure 88 which is required to overcome the friction of moving the work table i5 under idle conditions.

It is to be noted that the pressures 36' and Si are of an intermediate amount so that an inter-l mediate pressure is at this time being applied from the cylinder chamber 3l to the pressure chamber 'i3 or the modulating valve 65 and an intermediate pressure from the cylinder chamber 33 is being applied in the pressure chamber 8f of the other valve l5. These Valves are so constructed that an intermediate pressure applied to the `chambers 'i3 or 84 is insuicient to overcome the corresponding compression springs and 8c sufficiently to permit flow of fluid past the corresponding ends i2 and 'i8 into the respective discharge openings 5t and 8i or the valves. In other words, if pressure is applied only to the chambers 'i3 or 8d no flow can take place between the respective lines 'l to 54 or 82 to TI.

When the hydraulic motor is being driven by the table feeding movement to the left pressure is being delivered into line 66 by the hydraulic motor 55 so that fluidpressure will increase in the pressure chamber 55 of the Valve 66 which `will assist the pressure already existing in the chamber i3 to move the plunger 6l axially to the leit, Figure l, so as to permit this iiuid 55 to escape past the edge 'fl into the chamber 69 and the line il to the return line 59 connected to the intake or" the hydraulic motor 55. Under these conditions variation in pressure in the chamber 53 of valve 56 varies the resistance to flow of iiuid between lines 5ft and l-U by axially changing the position of the plunger 5i and opening between the edge TH and the end i2 of the plunger, thereby similarly varying the opposing torque of the 'i motor 55 reacting against the work table. The line 59 at this time being an intake line will have reduced pressure so that the pressure in the chamber 'iii of the other Valve 'l5 will be low with the result that the spring 8E) will be able to move the plunger axially to the left, Figure l, to close off the iiow of fluid between the line 62 and the line 'El under these conditions. Thus, during normal feeding of the work table before the work has engaged the tool there will be a circulation 5 of fiuid from the line 69 through the valve 66 to the line 55 with a moderate back pressure being maintained in the line 66 -by means of the spring 63 restricting the opening at the edge ll in the valve 66.

n instances where normal upcut milling is to be done with the cutting action opposed to the feeding force, as the workpiece W2 engages the milling cutter la the cutting force will directly oppose the movement of the piston i2 to thereby increase pressure in chamber 5I while decreasing complementarily the pressure in the chamber 33 as indicated in Figure 2. There will then exist a pressure in chamber 5I at some point 89 and a pressure in chamber 33 at some point 95 indicated in Figure 2. Increase in pressure in the chamber 5i will 'ce transmitted through the lines 38 and M to chamber 73 in valve 65 to move the plunger 6l' to compress spring 68, decreasing the fluid resistance at the edge 'il in the valve to therebyA decrease pressure in the line 60 and reduce the opposing torque of the hydraulic motor 55.

Variations in the cutting force which take place during the machining cycle may readily cause rapid pulsating changes in pressure in the cylinder li between the point 36 and 89, and 8i and 9U, Figure 2, with the result that the work tab-le due to the compressability of the fluid in the chambers 3l and 33 may not move uniformly and smoothly to efect the high degree of inishV desired on the workpiece. This undersirable operation is automatically compensated for since any change in pressure in the chamber 3| is immediately reflected in the control chamber 1,3 and likewise in the relative positioning of the Valve plunger 6l so as to automatically vary the resistance to flow between lines 64 and 19 to instantly oppositely vary the pressure in the line 56 and the eiective torque of the motor 55 reacting' on the work table Il. Thus, changes in the pressure in the actuating cylinder Il are trans mitted by means of the modulating valve 66 to cause complementarily varying degrees of opposing force to be transmitted by the hydraulic motor 55 directly to the work table. Whenever the pressure is suddenly released in the actuating cylinder by a cutting tooth leaving the workpiece momentarily, the hydraulic motor 55 at this time is immediately rendered effective to take up the force that was released by the cutter and to thereby maintain a uniform restricting force on the work table despite intermittent cutting action being applied by work andtool.

This arrangement is well adapted to instances where down cut milling is to be understaken. In down cut milling there is a rapid changeover of operating conditions for the work table from idle actuation to negative Work resistance conn ditions as the cutter engages the work. This device is instantly responsive to these changes to provide a counter opposing force to the feeding movements as the cutter engages the work and automatically decreases this opposing force when the hooking-in action of the down cut milling` operation decreases as idle cutting conditions arc approached. AS the work piece begins to en gage the cutter` during the machining operation the cutting forces tend to assist the feeding forces with the result that pressure will decrease in the chamber 3l and will increase in the chamber 33 of the cylinder H. A pressure as indicated at some point 9|, Figure 2, may develop in the chamber 3i while a pressure at some point S2 may develop in the chamber 33. It is to be noted that a decrease in pressure in the chamber 3| likewise decreases the pressure in the chamber 73 of valve S5 so as to permit the plunger under the action of the spring 63 to increase the resistance at the edge 'i I, thereby building up pressure in the line Bil to oppose rotation of the mom tor 55 and thereby cause the motor to maintain the necessary back pressure against the worl table in opposition to the varying cutting forces between work and tool. The valve 67 readily modulates or automatically adjusts itself rap-idly back and forth in strict accordance with the changes in cutting forces developed by intermittent cutting action by the teeth on the work so as to maintain an eiective uniform feeding mction by the cylinder il. Thus, in this case of down milling, whenever the cutting forces tend to pull in the work to the cutter the pressure decrease in the chamber 3i of the cylinder H is utilized to automatically control the hydraulic motor 55 to instantly oppose the motion of the work table in proportion to the pulling-in ac-` tion developed between cutter and work at this time.

When feeding motion is to be eifected in the opposite direction as when positioning the control lever 26 of the valve 2| in the position 25d, the cylinder chamber 33 is then utilized to control the valve l through the pressure control chamber 3i! to effect the modulated control of the hydraulic opposer motor 55 in the same fashion as that just described for the valve 55. The valve' underthis latter condition of operation, of course, would be rendered inoperative by the reduced pressure in the chamber i3 so as to prevent iiow of fluid from the line li! to the line 64. Inthis latter case fluid will be discharged from the motor 55 into the line 59 and intake into the motor 55 will be received from the line 6l).

In order to automatically permit a free movement of the work table ill at any time at rapid traverse movements, there is provided a short circuiting or rapid traverse control valve 93 for the hydraulic opposer motor 55 having a control plunger .fill which is constantly urged in one direction by the compression spring 95 and which may be actuated in the other direction by fluid pressure from line 6| connected to actuate the plunger axially against the spring 95 by a line 9B. When the control lever 26 of selector valve 2| is in a neutral position intermediate 26e and d only a low fluid pressure is applied to the line BI and the line 96 from the rapid traverse pump I9 as determined by the setting of the low pressure relief valve 24. This relief valve 24 is set at a pressure which is insufficient to axially shift the plunger 94 of the short circuiting valve 93 against its spring 95. However, when the control lever 26 of the selector valve 2l is moved to either rapid traverse position 26o, or 25e, the higher pressure relief valve 22a is now effective to control the output pressure from the rapid trav-` erse pump I9 so that a higher pressure now exists in the line 6i during rapid traversing of the piston I2 in the cylinder Il. This latter pressure as determined by the higher pressure relief valve 22a is suiiicient to cause the plunger .'34 of the short circuiting valve to be shifted against the spring 95 with the result that the line 59 is connected by means of the branch line 91 and the annular groove 98 of the Valve plunger 94 to the branch line 99 which, in turn, is connected to the line 50 so there now is free, unrestricted flow between the lines Sil and 59 so that under rapid traverse conditions there is no restriction imposed upon the work table Il) by the opposer motor 55. This valve automatically cuts out the shortcircuit between `the lines 59 and 5i! of the motor 55 when either feed position or stop position is selected as the low pressure relief valve 24 is then operatively connected to reduce the pressure in line 5i and the branch line 96 to permit the plunger to return to the blocked-off position shown in Figure 1.

There has thus been provided in a hydraulic feeding system for a machine tool a hydraulic control and opposer mechanism which is readily sensitive to changes in the cutting forces applied to the feeding mechanism of the machine to maintain a smooth uniform relative feeding of work and tool.

What is claimed is:

1. In a milling machine having a work table, a cutter support associated with said work table, a

hydraulic motor including a piston and 'cylinder for actuating said work table, a locked hydraulic feeding circuit connected to said cylinder at opposite sides of said piston to effect complementary pressure differences in said cylinder for effecting relative feeding movement in said work table, a separate hydraulic opposer motor, gearing interconnecting the motor and said work table whereby the motor is driven by movement of the table, ailuid circulating circuit connected to said motor, and a variable resistance means in said circuit reacting on the flow of iiuid in said circuit when said motor is being driven by said work; table, and pressure connections between the locked circuit and said variable resistance means whereby said means are controlled by variations in the fluid pressure in said actuating cylinder circuit.

2. In a hydraulic control and feeding mechanism for a milling machine having a work table, a cutter support associated therewith, and a hydraulic actuator for said work table including a cylinder, a piston connected to said work table, a locked hydraulic feeding circuit connected to said cylinder for effecting differential complementary pressures each side of said piston to cause feeding movements in said work table, a hydraulic opposer mechanically connected to said work table for actuation by movement of thetable, and a modulating control valve hydraulically connected to said locked hydraulic feeding circuit, for regulating hydraulic flow through said opposer in response to changes in fluid pressure in said cylinder.

3. In a hydraulic control and feeding mechanism for a milling machine having a work: table, a cutter support associated therewith, and a hydraulic actuator for said work table including a cylinder, a piston connected to said work table, a locked hydraulic feeding circuit connected to said cylinder for effecting differential complementary pressures each side of said piston to cause feeding movements in said work table, a hydraulic opposer mechanically connected to said work table for actuation thereby, a modulating control valve hydraulically connected to said locked hydraulic feeding circuit, for regulating hydraulic flow through said opposer in response to changes in fluid pressure in said cylinder, and common uid pressure supply means for said locked hydraulic feeding circuit and said hydraulic opposer.

4. In a milling machine, a work table, a hy" draulic cylinder for actuating said table in feeding movements, a locked hydraulic feeding circuit connected to said cylinder, a hydraulic opposer motor mechanically connected to be driven by the movement of said table, a iiuid circulating opposer circuit connected to said opposer, a common fluid supply source for said lockedhydraulic feeding circuit andsaid opposer circuit, and a control Valve to vary the fluid pressure in said opposer circuit in accordance with variations in pressure supplied to said hydraulic cylinder when feeding said work table.

5. In a milling machine, a work table, a hydraulic cylinder for actuating said table in feeding movements, a locked hydraulic feeding circuit connected to said cylinder, a hydraulic opposer motor mechanically connected to be driven by the movement of said table, a fluid circulating opposer circuit connected to said opposer, a. common fluid supply source for said locked hydraulic feeding circuit and said opposer circuit, a control valve to regulate now in said opposer circuit in accordance with variations in pressure supplied to said hydraulic cylinder when feeding said work 1 table, a rapid traverse control circuit connected to said cylinder to effect rapid traversing movements of said work table, and control means coupled with said opposer circuit to render said control valve therein inoperative when said Work table is being actuated at rapid traverse movements.

6. In a milling machine having a work table, a hydraulic motor including a piston and cylinder for actuating said work table, a hydraulic opposer motor, a mechanical drive between said opposer motor and said Work table, a hydraulic feeding circuit associated with said cylinder, a hydraulic opposer circuit associated with said opposer motor, a common source of fluid pressure supply for both of said circuits, and a variable hydraulic pressure controi means in said opposer circuit actuated by changes in pressure in said feeding circuit during the feeding movement of said table to vary the reaction of the opposer motor against the table by Way of the mechanical drive.

7.V In a milling machine having a Work table, a hydraulic motor for actuating said Work table, a hydraulic opposer motor connected to said work table and actuable thereby, a hydraulic feeding circuit associated with said first motor, a hydraulic opposer circuit associated with said opposer motor, a common source of iluid pressure supply for both of said circuits, a variable flow control means in said opposer circuit actu- 3g able by changes in pressure in said feeding circuit during the feeding movement of said table, a hydraulic rapid traverse circuit connected to said cylinder, a selector valve for alternately rendering said feeding or rapid traverse circuits operative,

and means to automatically render said iiow control means ineffective when said rapid traverse circuit is operative.

8. In a milling machine having a work table,

a hydraulic motor for actuating said Work table A including a cylinder and-a piston movable therein, a locked hydraulic feeding circuit connected to supply fluid pressure to said cylinder for feeding in one direction or in the opposite direction, a hydraulic opposer motor mechanically connected to said Work table for actuation thereby,` a hydraulic fluid opposer circuit connected to said motor, a control valve in said opposer circuit controlled'by variations in fluid pressure on one side of said piston to restrict flow of fluid in said opposer circuit when said table is feeding in one direction, a second control valve in said opposer circuit controlled by Variations in fluid pressure on the other side of said piston to vary the rate of flow in said opposer circuit, said valves being connected in said opposer circuit so that one or the other of said valves are automaticallyrendered effective depending upon the direction of feeding of said work table.

9. In a milling machine having a Work-table, a hydraulic motor for actuating said work table including a cylinder and a piston movable therein, a locked hydraulic feeding circuit connected to Supply ,uid pressure to said cylinder for feeding the table in one direction or in the opposite directive to restrict free rotation of said tion, a hydraulic opposer motor mechanically connected to said Work table for actuation thereby, a hydraulic fluid opposer circuit connected to said motor, a control valve in said opposer circuit controlled by variations in iluid pressure on one side of said piston to restrict flow of fluid in said opposer circuit when said table is feeding in one direction, a second control valve in said opposer circuit controlled by variations in fluid pressure on the other side of said piston to restrict flow of fluid in said opposer circuit when said table is feeding in the other direction, said Valves being connected in said opposer circuit so that one or the other of said valves are automatically rendered effective depending upon the direction of feeding of said work table, Va rapid traverse circuit associated with said hydraulic cylinder for effecting rapid movements of said Work table in either direction, and a short circuiting valve coupled to the opposer circuit rendered operative by the application of rapid traverse pressure to said hydraulic cylinder to automatically render said modulating valves ineffective to restrict free ilow of fluid in said opposer circuit.

10. In a milling machine having a frame, a Work table reciprocable .on said frame, a hydraulic cylinder on said frame for reciprocating said table, a hydraulic opposer motor on said frame connected to be driven by the movement of said table, a source of iluid pressure connected to operate said cylinder including a low pressure rapid traverse circuit and a high pressure locked feeding circuit and a selector valve to render one or the other of said circuits operative, an .opposer circuit connected to said opposer motor, a pair of control valves in said opposer circuit each automatically rendered effective for one direction of feeding movement of said table variably to restrict rotation of said opposer motor in response to changes in fluid pressure in said feeding circuit, and means rendered effective by the operation of said selector valve when moved to render said rapid traverse circuit operative to automatically render said control valves ineffecopposer motor. Y

HANS ERNST. ALBERT `H. DALL.

REFERENCES CITED The following references are of record in the file of this `patent:

UNITED STATES PATENTS Number Name Date 1,978,350 Martellotti Oct. 23, 1934 1,996,466 Ernst Apr. 2, 1935 2,028,766 Ernst et al. Jan. 28, 1936 2,035,388 Kearney Mar. 24, 1936 2,216,550 Ernst Oct. l, 1940 2,267,696 Groene et al Dec. 23, 1941 2,309,637 Fickett et al. Feb. 2, 1943 2,363,706 Svenson Nov. 28, 1944 2,448,426 Galloway Aug. 31, 1948 

